My MC isn't faithful though. He does cheat, just not with characters that look like children. Just wanted to clear up that ASSumption as I never made any arguments disputing cheating as a focus. There's the sister, the prostitute and the co-worker so far. Your comment went from "will the MC cheat? That means will he fuck his step-daughter!" When there are other options to choose to cheat with. MC will bang them all as long as they are adults and not built like a Jim Henson muppet. That's how choices work in these games. YOU choose the focus by the decisions YOU make. The game doesn't choose it for you.
I wouldn't argue against anything you're saying. She's definitely a main character, but not THE main focus unless you make her so. The Wife's sister is getting more content which I like, and wish they'd just give us more tbh.
For my own personal tastes, the one mistake the game has made was making the step-daughter the least attractive person in the game. Super easy to tell to fuck off and continuing chasing the other women.